Integrated optics is a term used to describe a rigid structure which has a plurality of waveguides defined therein, such as in the well-known arrayed waveguide grating (AWG). Such arrayed waveguide grating devices are commercially available and are typically fabricated by well-known photo-lithographic techniques used to configure film overlays on a silicon substrate. Copending application Ser. No. 09/574,840 filed May 19, 2000 for the inventors of the invention of the present application and assigned to the assignee of the present application, discloses a process for configuring thin films of sol-gel into a variety of structures useful for transmission of optical energy.
At the present time, films prepared from sol-gel with the required thickness and flatness to create integrated optic waveguiding structures can be produced by conventional spin coating techniques using standard semiconductor type coating equipments, such as those commercially available from Silicon Valley Group (SVG), Suss Micro Tec, Inc., or other manufacturers. While the sol-gel is in liquid form, centrifugal force acts as a surface leveling agent on the dispensed liquid. Unfortunately, the tendency of the liquid film toward uniformity does not apply at the outer edge of a spinning disk because the surface of the liquid film must curve and intersect the substrate somewhere in the vicinity of the edge. An effect may be produced where the outer periphery of the sol-gel has a different thickness than the rest of the surface, in the industry sometimes referred to as “edge bead” formation. This variation on the sol gel film thickness at the edge of the wafer often results in the formation of micro-cracks at the edge of the film. These micro-cracks further propagate onto the film structure during the subsequent heat treatment steps resulting in complete catastrophic failure of the film. Once the sol-gel film has cracked, all of the effort that has gone into the production of high-definition, sub-microns structures is wasted as the wafer becomes useless and must then be discarded. Furthermore, if a contact photo mask is to be used with a photosensitive sol gel to create a waveguide structure, this rim must be removed as otherwise there will be gaps between the mask and the photosensitive surface through which light may enter and substantially degrade the image quality and resolution of the photolithographed waveguide pattern.
It would be of great advantage to be able to fabricate glass integrated optical devices using a sol-gel process that provided extremely flat surfaces onto which submicron dimensioned features could be defined without the danger of the sol-gel film cracking or absorbing efficiency-reducing amounts of power.